1. Field of the Invention
The disclosed technology relates to the field of sample characterization, and more particularly, to methods and systems for spectroscopy based characterization, such as surface enhancement Raman spectroscopic characterization.
2. Description of the Related Technology
Nano-apertures in metal films attract huge interest in sub-wavelength plasmonics. These nano-apertures find applications in emerging fields such as molecular spectroscopy and nanoparticle optical trapping. The excitation of surface plasmons in such apertures results in large electromagnetic field enhancements, which are useful for applications such as surface enhanced Raman scattering (SERS).
Recently, a gold nanoslit-cavity is developed on a freestanding silicon membrane based on long (several micrometers) slits in a gold film. A strong field enhancement in the nanoslit is demonstrated by Chen et al. and applied for SERS. It could be further improved by equipping it with gratings for SPP excitation or reflection.
The use of individual nano-apertures is furthermore considered as an effective method for single molecule analysis, as analyzing the ionic current that flows through a nanopore can reveal the presence of single molecules in real time. However, although this technology can efficiently be used to show the presence of molecules in a nanopore, it currently lacks the ability to reliably identify the specific molecules.
For single molecule level detection using SERS, it was stated in prior art that a long slit having a length in the range of 2 to 100 μm and a width of around 2 to 5 nm is needed to generate a strongly enhanced optical field. However, to reproducibly and uniformly manufacture slits with such a small width (5 nm range) with a small standard deviation is a big challenge for the standard available state of the art of nanofabrication. Furthermore, for a nanofluidic application, a long nanoslit is difficult to manipulate single analyte molecules as there is an uncertainty of the location and the amount of molecules along the slit.
There is hence a need to improve the geometric design of the nanoslit while at the mean time maintain or further improve the electromagnetic field and transmission resonances.